Test and validate regular expressions with real-time match highlighting.
Matches
Count14
Flagsg
Match Details
Match 1: The
Index: 0
Match 2: quick
Index: 4
Match 3: brown
Index: 10
Match 4: fox
Index: 16
Match 5: jumps
Index: 20
Match 6: over
Index: 26
Match 7: the
Index: 31
Match 8: lazy
Index: 35
Match 9: dog
Index: 40
Match 10: This
Index: 45
Match 11: is
Index: 50
Match 12: a
Index: 53
Match 13: regex
Index: 55
Match 14: tester
Index: 61
Highlighted Text
The quick brown fox jumps over the lazy dog. This is a regex tester.
Enter a regex pattern and test string. The g (global) flag finds all matches; without it, only the first match is shown. Groups in parentheses are captured separately.
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What is the Regex Tester?
A regex tester is an interactive environment where you enter a regular expression pattern and test text, then instantly see which portions of the text the pattern matches. It eliminates the guesswork from writing regex by showing you exactly what your pattern captures, group by group.
How it works
Paste or type your regex pattern and your sample text into the tester. The tool runs the pattern against the text immediately, highlighting every match in the string and displaying match details (the full match, any captured groups, position, and length). If your regex syntax is invalid, the tool reports the error so you can fix it.
Examples
Input
Result
Notes
Pattern: \d{3}-\d{4} | Text: Call me at 555-1234 or 999-9999.
Matches found: 2 (555-1234 and 999-9999)
Tests phone number validation using character classes and quantifiers
Pattern: [a-z]+@[a-z]+\.[a-z]+ | Text: Email john@example.com for details.
1 match: john@example.com
Basic email pattern matching with character ranges
Pattern: (\w+)\s(\w+) | Text: Jane Doe meets John Smith.
2 matches with captured groups: (Jane, Doe) and (John, Smith)
Captures first and last names separately using parentheses
How to use the Regex Tester
Enter your regular expression pattern in the pattern field (e.g., \d+ for digits, [a-z]+ for letters)
Paste or type the text you want to test against in the sample text area
The tester immediately highlights all matches in the text
Check the match results panel to see captured groups, position, and length of each match
Refine your pattern by editing and testing again—changes apply in real time
Copy your final pattern once it matches exactly what you need
Benefits
Save hours of debugging—see regex matches instantly instead of running code or using trial-and-error
Learn regex interactively by watching patterns behave on real text
Catch syntax errors immediately with helpful error messages
Visualize captured groups to understand how your pattern breaks apart the text
Test edge cases and special characters without touching your production code
Tips & common mistakes
Common mistakes
Forgetting to escape special regex characters like . * + ? ( ) [ ] { } \ ^ $ | when you want their literal meaning
Using . which matches any character instead of \. to match an actual period
Testing only happy-path examples and missing edge cases like empty strings, special characters, or very long inputs
Tips
Use \b for word boundaries to match whole words only—useful for searching names or terms in sentences
Test your pattern on multiple text samples including edge cases to ensure it handles variation
Start simple and build up your regex step by step—test \d+ before moving to \d{3}-\d{4}
Use capturing groups (parentheses) when you need to extract specific parts of the match
Frequently asked questions
What's the difference between . and \. in regex?
. matches any single character except newline. \. matches a literal period. Always escape the period when matching URLs, file names, or decimals.
How do I match optional text?
Use ? to make the preceding item optional—e.g., colou?r matches both 'color' and 'colour'. Use * for zero or more, + for one or more, or {n,m} for a specific range.
Can I use regex to validate email addresses?
Simple patterns like [a-z0-9]+@[a-z]+\.[a-z]+ work for basic cases, but complete email validation requires complex regex or better yet, server-side verification of an activation link.
What are captured groups and why use them?
Parentheses () create captured groups, which isolate parts of your match. They're essential for extraction—e.g., (\w+)@(\w+) captures the username and domain separately so you can work with each independently.
Why is my pattern matching more than expected?
Regex is greedy by default—+ and * match as much as possible. Add ? after * or + to make them non-greedy (e.g., .*? matches the minimum). Test on your actual text to see what's captured.
Does this tester work with all programming languages?
Most languages (JavaScript, Python, Java, PHP, Go) use POSIX or compatible regex syntax and behave the same way. Some have minor differences in escape sequences or flag support, so verify on your platform if testing something language-specific.